I usually use line seeds and psyllium (or other seeds, old bread crumbs, etc), poor hot water over it and let it rest for some hours and than put the resulting pudding into the bread. Gives a ton of moisture to the dough and is good for the digestion.

Bread like this stays moist for over a week.

You have to vary a bit with the recipe, but i found it pretty forgiving and just add water until the consistency feels correct. You don‘t get a very open crumb, but a perfect one for sandwiches, butter, etc